Support OpenID Connect .well-known for simpler configuration

<!-- Please only use this template for submitting feature requests --> **Why is this needed**: Most IAMs that support OIDC/OAUTH support a [discovery endpoint](https://datatracker.ietf.org/doc/html/rfc8414) that allows clients to get important information about the IAM, such as the issuer name, token and auth URLs, etc. This greatly simplifies the configuration process. While support for this was added via the auth configuration form in the UI as mentioned in #27443, there still seems to be no way to utilize the discover URL through the TOML configuration file. According to the [announcement](https://grafana.com/whats-new/2024-09-24-openid-connect-discovery-url-for-generic-oauth/), it only appears to be supported via the form in the UI. **What would you like to be added**: The [OAUTH Configurations](https://grafana.com/whats-new/2024-09-24-openid-connect-discovery-url-for-generic-oauth/) would be expanded to support the discover URL. When set, it will no longer be required to manually set the token, auth, and api URLs. **Who is this feature for?** Any user using OIDC or OAUTH 2.0 who wants to configure auth in Grafana via the TOML configuration files.